Quantum Chemical Calculation of the Effects of H(2)O on Oxygen Functional Groups during Coal Spontaneous Combustion.

The effects of H(2)O on the low-temperature oxidation characteristics of coal have always been one of the keys in the research of coal spontaneous combustion, but most studies rely on experiments for macroscopic derivation, and theoretical researches at the microlevel are rarely mentioned. In this paper, phenylacetaldehyde, phenylethyl alcohol, phenylacetic acid, and ethylbenzene hydroperoxide were used as modeling compounds of coal molecules containing aldehyde (-CHO), alcohol hydroxyl (-OH), carboxyl (-COOH), and peroxide (-C-O-OH). The surface electrostatic potential (ESP), electron density of atoms in molecules (AIM), and reduced density gradient (RDG) of coal molecules were calculated by density functional theory (DFT), and the thermokinetic parameters of low-temperature oxidation of coal molecules with or without H(2)O were analyzed. The results show that the extreme positive and negative ESPs are located at the H and O atoms of oxygen functional groups (OFGs), respectively, which are the active sites for H(2)O adsorption. The AIM and RDG show that the phenylacetaldehyde···H(2)O complexes have two kinds of adsorption configurations with two and three hydrogen bonds, and that the phenylethyl alcohol···H(2)O complexes also have two kinds of adsorption configurations with one and three hydrogen bonds, and that both phenylacetic acid···H(2)O and ethylbenzene hydroperoxide···H(2)O only have one adsorption configuration, forming two and three hydrogen bonds, respectively. According to electron density ρ(r) and potential energy density V(r), the adsorption strength of H(2)O by four kinds of oxygen functional groups is ranked as -C-O-OH > -COOH > -OH > -CHO. The thermokinetic parameters show that H(2)O can increase the activation energy (ΔE) of the oxidation reactions of phenylacetaldehyde and phenylethyl alcohol, which can inhibit the reaction and decrease the activation energy (ΔE) of the oxidation reaction of phenylacetic acid and ethylbenzene hydroperoxide, which can promote the reactions.